Prior to this invention, gas seals have commonly utilized stationary and rotating rings of simple ring type geometry which maintain a lubricating film (gap) between their respective sealing faces by means of hydrodynamic fluid forces. The terms hydrodynamic and hydrostatic as used herein are meant to convey their conventional meanings (as discussed, for example, at page 661 of Principles and Design of Mechanical Face Seals, Lebeck, A., 1991; ISBN 0-471-51533-7). The stationary sealing ring (stator) is generally disposed in the sealing housing and the rotating sealing ring (mating ring) is generally disposed on and fixed to the shaft. Geometric symmetry of the mating ring and application of pressure balancing techniques about the mating ring, in the prior art, ensures the mating ring sealing face remains perpendicular to the axis of the shaft and parallel to the stationary sealing face throughout all operating conditions. Prior theoretical art shows that a slightly converging gap (converging coning angle) between the adjacent sealing faces is a fundamental requirement for stable seal operation. A slightly diverging gap between seal faces (diverging coning angle) causes hydrostatic and hydrodynamic fluid instability and destruction of the sealing faces due to touchdown and rubbing. A diverging gap is defined as where the axial distance between sealing face surfaces is smallest at the high pressure diameter. Prior disclosures by Wiese (U.S. Pat. No. 3,628,799) and Gardner (U.S. Pat. No. 3,804,424) infer that sealing face distortion must be minimized or neutralized for successful operation of the sealing devices disclosed. For example, in U.S. Pat. No. 4,212,475 (Sedy) it is stated that the inventor believes that seal failures may arise, in part, from the inability to maintain sufficiently parallel alignment of the non-contacting faces. Sedy then describes a seal with a non-distorting mating ring as well as a stationary ring (stator) with momentary or transient self alignment features based on generating interfacial hydrodynamic pressures in excess of pressures sealed. Those skilled in the art will realize that distortion of the mating ring during operation is prevented by utilizing a geometrically symmetrical mating ring and by balancing the pressure forces about the mating ring. Mating ring symmetry shown by Sedy is believed to result in the sealing face remaining essentially perpendicular to the axis of the shaft when the ring is subjected to centrifugal force due to rotation. A non-symmetrical mating rotor would cause the sealing face to tilt in a diverging or converging manner as speed is varied, resulting in changing stable and/or unstable operating characteristics throughout the seals operating range. The two o-rings shown by Sedy at the rear face and inside diameter of the mating ring provide a flexible mount to presumably enhance mating ring dynamic stability as well as seal the process fluid. Mating ring distortion is further prevented by a pressure balancing feature provided by the o-ring shown at the rear face of the mating ring. Although the function of this o-ring is not described by Sedy, its purpose is presumably to preclude the loss of fluid through the rear of the seal. Those skilled in the art will realize that the position of this o-ring at the rear of the mating ring also substantially prevents a diverging tilt, and unstable operation, of the mating ring when subjected to hydrostatic pressure. Symmetrical mating ring geometry and the rear o-ring position provide mating ring balancing features necessary to ensure stable seal operation in seals described in prior art. Stationary seal rings are generally not intended to compensate for gross mating ring tilt or excursions that would occur without implementation of these mating ring seal face alignment features. However, as noted above, numerous components are required in such prior art seals so as to reduce the tendency for the mating ring to tilt. This is disadvantageous because the use of such numerous components greatly increases the cost and operating complexity of the seal.
Accordingly, it is one object of this invention to reduce the number of components in the seal by utilizing a deliberately flexible mating rotor and a deliberately flexible stator.